Class 6 Science Chapter 8 Notes A Journey through States of Water
→ Water Vapour: It is the gaseous state of water.
Evaporation:
- The process of conversion of water into water vapour is called evaporation.
- Evaporation takes place from open surfaces of water all the time-day and night and at all temperatures.
- Evaporation of water takes place continuously from oceans, rivers, lakes, wells and seas which are called water bodies.
- Evaporation causes cooling because liquid molecules absorb heat from water or surrounding to be converted into vapour.
Evaporation depends upon the following factors:
(a) Temperature
(b) Surface area of water
(c) Speed of air over the exposed surface of water
(d) Humidity
Large surface area, high the temperature and high speed of air increases the rate of evaporation. Evaporation causes cooling effect. Lesser/the humidity faster will be the evaporation.
→ Condensation: The process of conversion of water vapour into liquid form of water is called condensation. For example, formation of tiny water droplets on the surface of leaves/flower petals. Formation of water droplets on the outside surface of glass containing ice-cold water.
Different States of Water:
Water is found in nature in all the three physical states of matter: solid (ice), liquid (water) and gas (water vapour).
I. Liquid state: The water that we use every day is a liquid. It is called liquid state of water.
II. Gaseous state: Water evaporates on heating. Water vapour is the gaseous state of water.
III. Solid state: On cooling the water turns into ice. Ice is solid form of water.
Differences between Different states of water:
| Property | Solid (Ice) | Liquid (Water) | Gas (Water vapour) |
| Shape | Retain its shape (fixed shape) | Does not have fixed shape(Takes shape of container) | Does not possess a fixed shape (Takes shape of container) |
| Volume | Fixed volume | Fixed volume | No fixed volume |
| Flow or Spread | Does not flow | Flows | Flows |
→ The different physical forms of water are inter-convertible. The easy inter-convertibility of water from one form to other form, makes its availability in all parts of the earth and throughout the year.
→ The different physical forms of water are inter convertible. The easy inter-convertibility of water from one form to other form, makes its availability in all parts of the earth and throughout the year.
→ Melting: The process of conversion of a solid into liquid state on heating is called melting.
→ Freezing: The process of conversion of liquid into solid state on cooling is called freezing.
→ Clouds formation: The water vapour in the air condenses to form tiny droplets of water, which appear as clouds.
→ Many small water droplets come together and fall as rain, hail or snow. The earth’s surface is hotter but as we go up in atmosphere the temperature gradually decreases. At the upper layer of atmosphere, where the temperature is very low, the vapour gets condensed into tiny water droplets and forms clouds.
→ Humidity: The amount of water vapour in the air is known as humidity. If the amount of water in the air is already high (more humidity), water evaporates slowly.
→ Groundwater: The water that seeps into the ground accumulates under the ground is known as groundwater. Groundwater is the source of wells and lakes. Groundwater is withdrawn through handpumps and tubewells.
→ Rain: If water droplets fall in the form of liquid on the surface of the earth it is called as rain.
→ Hail/Snow: If the size of frozen water drops is large, the solid form is called as hail. If solidification is in the form of light flakes, it is called snow.
→ Dew: Water droplets, especially during winter nights, formed by water vapour present in the air, are called as dew.
→ Water Cycle: The circulation of water between the earth surface and atmosphere is known as the water cycle. Water cycle helps in regulating weather on the earth. Water cycle is like a ring. In nature, the water cycle takes place from sea to land and back to sea again.
→ Conservation of Water: Water is abundant on Earth, but the usable supply is limited and is decreasing due to over-usage. With a growing population, the demand for water for drinking, food preparation, and industry is increasing. Conservation involves using water carefully, and efficiently, and avoiding waste. Successful conservation programs require everyone’s faithful participation.
→ How to Conserve Water: In the first place, make it a habit to close a water tap, immediately, after taking the required amount of water from it. Minimum quantity of water should be used for bathing, washing and cleaning purposes.